As well known, a standard configuration for a gas turbine envisages a plurality of blades solidly inserted into a rotor body. In particular, each blade comprises a fir-tree root which is retained into a correspondent fir-tree portion of the rotor body. The outer portion of the blade comprises an airfoil, shaped in a way to convert the kinetic and pressure energy associated to the hot fluid flow evolving in the machine to mechanical energy available at the rotor shaft, the blade airfoil being integral to the blade fir-tree root by means of a blade shank portion interposed there between. The pressure and temperature which arise in rotor cavities positioned between subsequent blades cause a leakage of hot fluid towards the shank and fir-tree portions of the blades. Such occurrence causes overheating of the blade parts, leading to deterioration in time of such components.
To solve this problem, a lock plate is generally provided to shield the blade fir-tree root and the blade shank from the hot flow coming from the adjacent rotor cavity. The lower portion of the lock plate is usually inserted in a groove engraved in the rotor body, whilst the upper portion is embedded in hook-shaped portion provided in the blade platform edge.
However, even though such arrangement determines a leakage reduction, it fails in providing a definitive solution to the problem. In fact, during normal operation of the machine, a temperature and pressure gradient between the fir-tree root and shank portion of the blade and the adjacent rotor cavity is usually experienced, such that a very high leakage occurs. It will be appreciated that manufacture tolerances between interconnected components cannot guarantee a perfect tightness. As a result, notwithstanding the presence of the lock plate at the interface of the rotor cavity and blade parts, a leakage of hot flow is still experienced causing a damaging effect on the blades and affecting the overall performance in time of the machinery.